/Engine/Source/Runtime/CoreUObject/Public/UObject/UObjectBaseUtility.h
Returns the custom version of the linker for this object corresponding to the given custom version key.
the custom version of the engine's package file when this object was last saved, or the current version if this object does not have a linker, which indicates that a) this object is a native only class, or b) this object's linker has been detached, in which case it is already fully loaded
int32 GetLinkerCustomVersion ( [FGuid](API\Runtime\Core\Misc\FGuid) CustomVersionKey ) const